Systems and methods herein generally relate to registration (alignment) of stacks of sheets, and more particularly to tampers to promote registration.
Many modern production devices output sheets of media, such as sheets of paper, transparencies, plastic sheets, ceramic sheets, metallic sheets, etc. These sheets are often output into stacks, and the stacks are more efficiently processed if all the sheets are aligned with each other. For example, many printing devices align a stack of sheets before stapling the stack.
In one example, a printing device may send the lead edge of paper into the throat of a stapler. In front of the staplers, there is commonly a narrow shelf that helps guide the paper into the stapler and that provides support for the front portion of the paper as it begins to accumulate. The majority of the sheet body is then dropped onto the stack of previously compiled sets. The top of the stack, however, should not be located below the narrow shelf and staplers (because this is helpful for ejecting the newly compiled set onto the stack). This height delta can cause sheets to “walk downhill” as the top sheet of the set is tamped, creating angled, poorly registered sets. Furthermore, this height delta grows larger as small stapled sets begin to develop staple build-up.
Additionally, machine vibrations can cause sets of sheets to move away from the registration wall during tamping because there is nothing constraining the set in the process direction. Also, stepper motors can lose step counts due to rapid changes in motion, which result in mistimed and insufficient tamping.